I. Field of the Invention
The present invention relates generally to valves and, more particularly, to an adjustable seat assembly for such valves. While the seat assembly can be used in connection with any type of valve, the seat assembly is, preferably, used in connection with a ball valve and, more preferably, in connection with a top entry ball valve.
When used in a ball valve, the seat assembly of the present invention facilitates removal and insertion of the ball from the valve body, without the use of complex tools or equipment as heretofore required. In the case of other types of valves, the seat assembly facilitates insertion and removal of the valve component which directs the fluid flow. This, in turn, provides for easy replacement of the valve's seats. Moreover, the seat assembly provides for a rather precise and accurate adjustment of the ball/seat interface load over a wide range of pressures.
II. Description of the Prior Art
Valves, especially ball valves, are commonly used in coal gasification and liquefaction plants, nuclear facilities and the like to control the flow of liquids or gases. It is necessary, especially in a nuclear facility, that the valves do not leak or that the amount of leakage be minimal.
Many valves, such as ball valves, are secured in the fluid line and therefore cannot be removed.
Valve seats are typically positioned to interface with the ball of the valve to minimize leakage of the fluid between the ball and the valve body. The valve seats can be made of any non-metallic material, such as, for example, an elastomeric or a polymeric material, or of a metal material, depending on the temperature range and type of the fluids flowing through the valve. These seats must be periodically replaced when worn. Therefore, it is desired to provide for easy and rapid replacement of the seat.
Furthermore, since seat replacement is both costly and time consuming, it is desired to extend the life of the seat as much as possible. To accomplish this, the interface load between the seat and the ball must be appropriately set to minimize the pressure on the seat while maintaining the effectiveness of the seal formed by the seat and ball.
Many ball valves include a plurality of springs positioned in axial alignment with the seat so a to force the seat against the ball to establish a sealing load at the ball/seat interface. See, for example, U.S. Pat. No. 3,891,183 titled Sealing and Seat Assembly for Ball Valve Construction, which issued on June 24, 1975 to Monroe J. Feiring, and which is owned by the assignee of the present application. Heretofore, replacement of the valve seat was very difficult and somewhat dangerous. One method of removing the seat requires a technician to go through the top or bonnet area of the valve with specially designed tools. One type of tool is designed with basically a right angle configuration and is applied through the bonnet to catch the top of the front of the seat. The seat is physically forced back, i.e. away from the ball, overcoming the force of the springs for a sufficient distance to provide clearance so that the ball can then be removed. Thereafter, the seat is removed.
This disassembly is problematic and dangerous due to the heavy loads and the expensive tools required to enter the valve through the bonnet and overcome the force of the springs. For example, it has been found that for a twenty-four inch valve there is required approximately ten thousand lbs. of force needed to push the seat assembly from the ball. Further, when the seat is placed in its operative position, it applies a pressure of approximately seven thousand lbs. on the ball.
Another type of tool consists of a pair of hydraulic or mechanical jacks which are placed in the valve body to simultaneously retract two valve seats. This type of tool is problematic since the jacks are difficult to align and, in addition, there is insufficient space in the valve to readily work with the tool.
Another method of removing the valve seat requires the tool to enter into the end of the valve and through the flow path to contact the valve seat. The seat must be constructed with groove portions to receive the tools. The seat is physically pulled back, i.e. away from the ball, to provide sufficient clearance to permit removal of the ball and thereafter removal of the seat. This disassembly is problematic since it is also necessary to overcome the forces of the springs to move the seat back, away from the ball. Further, this type of disassembly can only be used if the valve is of a type to permit access to the end of the valve. Many times to secure the ball valves in the line, the end of the valve becomes inaccessible so that this method of disassembly cannot be used.
In addition, the valves and their valve assemblies, do not, heretofore, provide means for adjusting the seat/ball interference load.